Although declining powers of memory and cognition have been well documented both in normal aging and in dementia of the Alzheimer type (DAT), questions about the integrity of the underlying perceptual processes have received less attention. There is increasing evidence of: (1) an overlap in the brain structures afflicted by pathology associated with aging and with DAT; (2) the importance of those structures to the mediation of visuospatial information processing. Based on these points, four large-sample studies (each with N=200) are proposed to investigate changes in visuospatial processes over the adult lifespan. Because of recent evidence that effects of aging increase in the "oldest old," particular attention will be paid to the young-old and old-old. Brain changes associated with the aging of visuospatial processing will also be examined by supplementing behavioral measures of response latency and sensitivity with measures of event-related potentials (ERPs) and positron emission tomography (PET). Seven groups of healthy adults aged from 18 to 85 and three additional groups of elderly adults subjected to rigorous medical screening will be tested on tasks requiring detection and discrimination of simple visual stimuli. Task difficulty will be systematically varied over the experiments from simple luminance detection and localization to spatially cued detection to spatially cued discrimination. PET measures of resting glucose metabolism and ERP measures of latency and amplitude will be used to determine the spatial and temporal properties of early visual processing in the intact, healthy brain over the adult lifespan. Comparisons will be made between task difficulty levels across studies to determine the threshold and extent of age-related changes in processing simple visual information in a spatial context. This research is important because little work has been done on age-related changes in visuospatial processing. Because both age and DAT result in pathologies in brain structures important in visual spatial processing, early vision may be the most appropriate system for distinguishing normal, healthy aging from the early stages of DAT. The proposed research is unique in its multidisciplinary cognitive-neuroscience approach, in which systematic investigation using multiple measures of behavior, electrophysiology and regional cerebral metabolism will provide converging information with the potential to maximize understanding of age-related changes in early visual processing.